1. Field of the Invention
The present invention relates to a near-infrared absorbing material comprising a phthalocyanine compound which can also be used as a recording material for use in an optical information recording medium, a photoelectric conversion material, and a material for use in an infrared filter; a phthalonitrile compound and a diiminoisoindoline compound serving as intermediates for producing such phthalocyanine compounds capable of absorbing near infrared rays; and methods of producing such phthalonitrile compounds.
In addition, the present invention also relates to an optical information recording medium which comprises as a recording material the above-mentioned near-infrared absorbing material comprising such a phthalocyanine compound.
2. Discussion of Background
Materials capable of absorbing near infrared rays find a variety of applications, for example, in (i) safe-light filters for photosensitive materials which are sensitive to infrared rays; (ii) infrared filters for controlling the growth of plants; (iii) materials for intercepting the heat rays in sunlight; (iv) infrared filters for protecting eye tissues from infrared rays; and (v) infrared filters for the light receiving elements of semiconductors. In addition to the above, a recording material of an optical information recording medium is one of the important applications of the above-mentioned near-infrared-ray-absorbing materials.
Conventionally, cyanine dyes, phenanthrene dyes, naphthoquinone dyes, pyrylium dyes and squarylium dyes are known as materials capable of absorbing infrared rays, In Japanese Laid-Open Patent Applications 55-97033, 58-83344, 58-224793, 58-214162, and 59-24692, optical information recording media are disclosed which comprise any of the aforementioned dyes as recording materials.
Each of the above-mentioned dyes, however, has its own shortcomings when used as a recording material in the optical information recording medium. More specifically, phenanthrene dyes, naphthoquinone dyes, and squarylium dyes have low reflectance although they can be readily vacuum-deposited. The low reflectance will bring about a low contrast between an information recorded area formed by application of laser beams and a non-information recorded area. This will cause inaccurate reproduction of the recorded information.
Pyrylium dyes and cyanine dyes are soluble in solvents, so that they can be applied by liquid coating. However, these dyes are so poor in light-resistance that they are readily caused to deteriorate when exposed to the light employed for the reproduction of recorded information, and exposed to natural light.
In contrast to the previously mentioned dyes, phthalocyanine dyes have remarkably high thermal stability and photostability, so that there are proposed recording media, each of which comprises a phthalocyanine compound in an organic-dye-containing thin film, as disclosed in Japanese Laid-Open Patent Applications 58-183296 and 58-37851. In spite of the above-mentioned advantages of the phthalocyanine compounds, they have a shortcoming in the productivity thereof. To be more specific, a thin film of such a phthalocyanine compound can be made only by vacuum-deposition because it is impossible to use a coating method due to the poor solubility in organic solvents. In addition, the phthalocyanine compound easily tends to cause association of the molecules thereof, so that high refractive index and high reflectance cannot be obtained when used in an optical information recording medium.
Recently, in order to increase the recording density in the field of information recording, a semiconductor laser beam with a specific wavelength, that is, 680 nm or less, which is shorter than the wavelength range of the laser beam used for a conventional optical recording disk has been put to practical use. However, any conventional organic-dye-containing thin film for use in the optical disk does not exhibit appropriate light absorption and reflection in the wavelength range of 700 nm or less. Namely, high-density recording has been limited because an appropriate recording material for use in the optical recording medium is not available.
Furthermore, a write-once CD-R (CD Recordable) comprising a substrate, an organic-dye-containing thin film, a metal reflection layer and a protective layer, which are successively overlaid in this order, is required to exhibit high reflectance in order to satisfy the CD standards. Therefore, there is a demand for development of an organic dye material which has high stability and is capable of exhibiting high refractive index in the wavelength range of the reproduction light, namely, in the range of 700 to 830 nm.
To prevent the association of the molecules of the phthalocyanine compound and also to obtain high refractive index thereof when used in an optical information recording medium, the introduction of a bulky alkoxyl group at the .alpha.-position of the phthalocyanine has been carried out. Further, there are proposed various recording media of CD-R type which can match the shorter wavelength of the laser beam by halogenating the phthalocyanine compound for use in the organic-dye-containing thin film, as disclosed in Japanese Laid-Open Patent Applications 3-62878, 3-215466, 4-348168, 4-226390, 4-15263, 4-15264, 4-15265, 4-15266, 5-17477, 5-86301, 5-25177, 5-25179, 5-17700, and 5-1272.
However, the above-mentioned conventional phthalocyanine compounds are still unsatisfactory as the recording materials for use in the optical information recording medium although the refractive index thereof is improved.